Science Questions

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Because most people use the brakes to slow down. I already know how the different types of braking systems work. I also know that it is possible to use the engine to slow down a car. All I wanted to know was how it worked.
 
Using the equation E=mc^2, you can figure that the amount of energy from only one kg corresponds to 25,000,000,000 kWh. Considering if you only used each particle only once during the power supply phase, you could drive the car for about 100, 000 years, without stopping.
 
That's if the water was traveling at the square of the speed of light...but you know, we can't do that. And I thought the equation for energy has never been fully proven?
 
MrktMkr1986
Because most people use the brakes to slow down. I already know how the different types of braking systems work. I also know that it is possible to use the engine to slow down a car. All I wanted to know was how it worked.
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What I found for diesel engines -
[font=Verdana, Arial, Helvetica, sans-serif][size=-1]Before we go any further, we should mention that an exhaust brake is not a noisy compression brake, or "Jake" brake such as used on diesel big rigs and dump trucks. A Jake brake works by using hydraulic pressure to momentarily open the exhaust valve at the end of the compression stroke, venting off the compressed air into the exhaust system. That’s where all the noise comes from. The braking of a Jake brake occurs because of the pumping loss compressing the air, and then eliminating the compressed air “rebound” on the power stroke. Additionally, there’s a pumping loss as the piston descends on the power stroke with both valves closed and no combustion.[/size][/font]

[font=Verdana, Arial, Helvetica, sans-serif][size=-1]An exhaust brake is a device that essentially creates a major restriction in the exhaust system, and creates substantial exhaust backpressure to retard engine speed and offer some supplemental braking. In most cases, an exhaust brake is so effective that it can slow a heavily-loaded vehicle on a downgrade without ever applying the vehicle’s service brakes. But what really goes on inside the engine when an exhaust brake is activated, and how does exhaust backpressure slow the engine with enough force to slow the entire vehicle?[/size][/font]

[font=Verdana, Arial, Helvetica, sans-serif][size=-1]Now let’s add an exhaust brake downstream from the turbocharger. An exhaust brake is basically a valve that can be closed in the exhaust system to restrict (but not totally close off) exhaust flow. This valve closes when the driver releases the fuel throttle. Under these conditions, the exhaust flow from the cylinders is bottlenecked and rapidly builds pressure in the exhaust system upstream from the exhaust brake. Depending on engine speed, this pressure can easily reach up to 60 PSI maximum working pressure. Maximum working pressure is limited as part of the design of an exhaust brake. In this example, that same 60 PSI also remains in the cylinder for the entire exhaust stroke (exhaust valve open) and exerts 60 PSI on the piston top to resist its upward movement. We can think of this as negative torque, slowing the engine for a braking effect. We might even think of this as just the opposite of the power stroke, and in effect, it is. Thus, you can see that simply restricting the exhaust flow can generate substantial braking. That’s what makes an exhaust brake so effective.[/size][/font]

[font=Verdana, Arial, Helvetica, sans-serif][size=-1]The above example is simplified, and it gives a good illustration of how an exhaust brake works, but there’s a little bit more you should know. Theoretically, if we completely closed the exhaust path, we could build very high exhaust pressure to act on the piston during the exhaust stroke for even greater braking. We could, at least in theory, slam on the exhaust brake to the point of sliding the rear wheels – not a good plan when towing a trailer downhill. Consequently, we want to temper the exhaust brake action for a reasonable, controlled degree of braking. Besides, an exhaust brake cannot close the exhaust system completely for a number of other good reasons. If the exhaust is completely closed, the pressure in the exhaust system will continue to rise until either the exhaust system ruptures or engine damage occurs. In fact, according to the factories, letting the pressure in the exhaust system exceed 40 PSI for Ford diesels, 55 PSI for the Chevy/GM DuraMax, or 60 PSI for Cummins diesels, can actually damage a diesel engine. Here’s how. If the pressure in the exhaust system, which also bears against the back side of closed exhaust valves in a multi-cylinder engine, exceeds the valve springs’ ability to hold the valves on their seats, the exhaust valves would be forced open and the pistons could strike the valves, causing severe engine damage. Consequently, an exhaust brake must vent some exhaust flow through the exhaust system to keep the peak system pressure below the danger point. The pressure at which the exhaust valves can be blown open depends on the valve spring seat pressure and size (area of the valve head) of the valves used. This is a carefully engineered setting on all Banks Brake applications: a careful determination is made to produce maximum practical braking without causing engine damage. If it weren’t for the potential valvetrain or exhaust system rupture problems, the exhaust brake system could be designed to create incredible engine braking force, theoretically going so far as to lock up the engine! [/size][/font]

Source - http://www.bankspower.com/tech_howexhaustbrakeworks.cfm
http://www.google.com/search?hl=en&q=%2Bhow+engine+braking+works
 
Firebird
...which would be true if the 1st Law of Thermodynamics applied to nuclear chemistry/physics. But it doesn't.

E=mc^2
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Energy = mass times the speed of light squared.

What has this to do with "Energy and matter can neither be created nor destroyed, merely changed into other forms"?
 
PublicSecrecy
I thought it was inertia, torque, velocity, and something...

[Edit] And friction. Without friction the car would go forward all the time...friction is what keep the tires in contact with the road (and gravity too) [Edit]
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Yeah its friction, but I was hoping someone would ssay centrafugal force because that doesnt exist :(. meh
 
PublicSecrecy
That's if the water was traveling at the square of the speed of light...but you know, we can't do that. And I thought the equation for energy has never been fully proven?
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Water travelling at the speed of light...:lol: your joking right?
The C is only used in that equation as a constant (a universal constant), it has nothing to do with velocity. Einstein proposed that time was not constant, only the speed of light was, so time would have to slow down to accommodate light being constant as your speed increased (Special Relativity).

It's an equation, not a theory and it is reliable. It's used to calculate how much energy a nuclear device will give off. For example one form of fission involves Uranium 235 splitting into Rb 89 and Ce 144

1 neutron + U 235 --> Rb 89 + Ce 144 + 3 electrons + 3 neutrons

To calculate the amount of energy released per mole of Uranium 235, scratch head lots or jump to this link ;)

Short story...its lots! 1.811 x 10^10 kJ/mol of U-235

keram
Yeah its friction, but I was hoping someone would ssay centrafugal force because that doesnt exist . meh
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centrifugal force is the resulting opposite reaction to centripetal force ;) Usually demonstrated by swinging an object round your head on a piece of string...note: the string cannot push it can only pull So you cannot apply centrifugal force, but you can feel it as it reacts to the centripetal. One of Newtons laws of motion, every action has an opposite and equal reaction. :)
 
What caused the Big Bang? (if there really was a big bang)

Astronomers/scientists say the big bang was triggered by a reaction between two or more foreign objects, yes?

Well, they also say the big bang created all matter and was the very start of time.

So, for the initial reaction to have occured, there had to be some matter to react. But the big bang created all matter.

And the theory of the origins of the universe goes on to say that the big bang "created" time. Again, the astronomers/scientists theory goes out the window. Because, for the said reaction to take place, there must be time. Without time, absolutely nothing would happen. So how did the reaction occur in a period of no time???

Explain your reasoning.
 
Famine
Energy = mass times the speed of light squared.

What has this to do with "Energy and matter can neither be created nor destroyed, merely changed into other forms"?
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First of all the First Law of Thermodynamics, the Law of Conservation of Energy, says absolutely nothing about matter.

E = mc^2 has a lot to do with "Energy an matter can neither be created nor destroyed, merely changed into other forms", since, after all, mass is the numerical representation of matter's resistance to a change in motion.

Mass "is" matter.

Let's take John Cockroft and Earnest Walton's confirmation of Einstein's E=mc^2 as an example of what the hell I'm talking about:

Cockroft and Walton built their particle accelerator at Cavendish Laboratory in 1932. Through a series of voltage dividers they gave a proton enough energy to cause fission when it collided with a Lithium-7 isotope. It produced two alpha particles (helium).

p + Li --> 2He

Matter, and therefore mass, should have been conserved.

The mass of Lithium-7 is 7.016003amu, the mass of a proton is 1.007277amu, and the mass of one alpha particle is 4.00260amu. Therefore the total mass of the reactants is 8.02328amu, while the mass of the products is 8.00520amu.

Energy was not conserved in this reaction. As you can see matter (mass) isn't conserved either. So, what happened to the 0.01808amu's worth of matter? It was "destroyed". It wasn't matter anymore.

According to Einstein's Theory of Special Relativity, that mass was released as a product of the reaction, as energy. Matter is energy. Energy is matter.

How much "matter" became "energy" as a product of this collision?

E=mc^2



Tacet_Blue's link describing the fission of Uranium-235 is maybe (probably?) a better explanation than mine.
 
Tacet_Blue
centrifugal force is the resulting opposite reaction to centripetal force ;)
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It's a perceived force. It doesn't actually exist.

Firebird
Mass "is" matter.
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Oh no! Schoolboy error!

You are correct to say that matter and energy are interchangeable - hence the First Law of Thermodynamics - but mass and matter are not.

Matter can have zero mass - take the electron neutrino (and electron anti-neutrino), for instance. They have a zero rest mass - and handily, by applying Einstein's famous equation to the First Law of Thermodynamics, photons, which are energy and therefore matter, have a zero rest mass too.
 
keram
Whats the force that stops a car going forward when it turns a corner at speed. Its not what you think :P. Famine will probably know though :(.
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The force that changes the direction of the car when taking a corner is called centripetal force, due to the centripetal acceleration and the mass of the car+driver+whatever else is in the car. There is not such a thing as centrifugal force, as many might think. What we experience as "centrifugal" (hence pulling our body in the direction of the normal line to the curve, opposite to the instantaneous center of the curve) is nothing but our own inertia. When a body is moving toward one direction, it wants to keep doing that. Newton 1st Law: "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." In laymen's terms: "An object that's going straight, wants to keep going straight, unless a force stops it, makes it turn, or upsets its uniform condition." Hence, before you start a turn, your car (and your body in it) are going toward one direction; once you start the turn, your car is turning (due to the centripetal accleration), but your body wants to keep going towards the initial direction. Therefore, it seems like you are being pulled away from the turn. That sensation is due to inertia.

By the way, on a perfectly circular turn, the centripetal acceleration is equal to v^2/R, where v is the velocity of the object(s) moving (you+your car+whatever else is in it - you are all moving at the same velocity, unless you are walking inside your vehicle :D or unless the objects in your car are sliding around because you took the turn too fast :D) and R is the radius of the curve. Hence, the centripetal force is equal to m*v^2/R, where m is the mass of the object(s) going on that circular path (you+your car+whatever else is in it). If the curve is not perfectly circular, then replace R with rho, where rho is the instantaneous radius of curvature...

rho = [1 + (dy/dx)^2]^(3/2) / | d^2 y / dx^2 |

Where | | is the absolute value, dy/dx is the first derivative of y with respect to x and d^2 y / dx^2 is the second derivative of y with respect to x.
In this case you need to know a function that describes the path of the curve.

Enough physics/calculus... for now :sly:

EDIT: And by the way, the reaction to the centripetal force would be the static frictional force, provided by your tires: f = mu_s * N, where mu_s is the static friction coefficient, and N is the normal force, equal and opposite to the object's weight (m*g). So, centrifugal force does not exist, not even as a reaction force.

The Wizard.
 
Famine

Matter can have zero mass - take the electron neutrino (and electron anti-neutrino), for instance. They have a zero rest mass - and handily, by applying Einstein's famous equation to the First Law of Thermodynamics, photons, which are energy and therefore matter, have a zero rest mass too.
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Oh, for Christ's sake... :rolleyes: I'm not going to debate quantum theory with you.




The original question:

"What do you get when you destroy mass?"

The correct answer: energy.
 
Firebird
Oh, for Christ's sake... :rolleyes: I'm not going to debate quantum theory with you.
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Why not?

Could it be because you said mass = matter when in fact it doesn't?

You could at least have pointed out that neutrinos (and anti-neutrinos) have mass when in motion (at c) and there is no known way to slow them down - or that the Super-Kamiokande collector hints that electron neutrinos at least (and by extension the muon and tau neutrinos) may have a rest mass of "less than 1x10^-3 eV". Or entered into a lively debate about whether anti-matter or dark matter have mass (no and yes, in that order).

Firebird
The original question:

"What do you get when you destroy mass?"

The correct answer: energy.
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It's STILL not correct. When you attempt to destroy matter you get energy. However, matter and energy are freely interchangeable (General Relativity) and neither can be destroyed (First Law of Thermodynamics) so the question makes no sense even if the word "mass" is substituted for "matter". Which it can't, since mass is not necessarily matter - as shown above.
 
PublicSecrecy
...and how do u show square root on the computer?
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Unless you copy & paste the actual square root symbol, you can substitute it by typing "sqrt"

sqrt 16 = 4

sqrt 121 = 11

and so on...
...__________
\/
 
&#8730; <– Copy-paste (I did it on a Mac, so I can't give you the Windows alt code nonsense).
 
PublicSecrecy
ß is a double "S" sound in German?! sweet. Thanks for the link guys! and thanks sage!
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Didn't know that, I learned it in German last year. You can find some other odd letters from other languages as well.
 
does anyone know what hydrotetrachloride is? I found some unmarked can of it and when i sprayed it, it froze whatever got sprayed by it...So i promptly went out and started freezing ants, beetles etc. :D
 
Cool! Where did you find it? It sounds like some chemical mixed with chlorine. Maybe hydrogen and chlorine. Chlorine seems like it will kill anything if there is enough there. I think you will have to ask Famine or something. What did the label say? Was there any product name on it?

Edit - I searched on the internet and it thought it should be "hydro tetrachloride." That makes me think the hydro is like hydrogen or something. I don't know what tetra is and chloride being chlorine.

Edit - I don't know what hydro is, most likely hydrogen, but tetrachloride might mean four atoms of chlorine.
 

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